The invention is based on a fuel supply system for delivering fuel for an internal combustion engine set forth hereinafter.
Up till now, there have been fuel supply systems in which a first fuel pump delivers fuel from a fuel tank to a second fuel pump by way of a fuel connection. For its part, the second fuel pump delivers the fuel via a pressure line to at least one fuel valve. Normally, the number of fuel valves is the same as the number of cylinders of the engine. The fuel supply system can be designed so that the fuel valve injects the fuel directly into a combustion chamber of the engine. During operation of this fuel supply system, a high pressure is required in the pressure line leading to the fuel valve. For safety reasons, and due to leaks of the fuel valve into the combustion chamber which can never be completely prevented, it is useful after the engine is shut off to either completely or at least largely reduce the pressure in the fuel connection and in the pressure line of the fuel supply system.
When the engine is shut off, if the pressure in the fuel supply system is largely or completely reduced, then a vapor bubble can form in the fuel connection between the first fuel pump and the second fuel pump or in the pressure line between the second fuel pump and the fuel valve. The size of the vapor bubble or the number and size of the individual bubbles of the vapor bubble depends among other things, particularly on the temperature prevailing in the engine compartment after the engine has been shut off. The vapor bubble must be bled out from the lines or be compressed before a renewed starting of the engine. Since the delivery quantity of the second fuel pump is relatively slight during the starting of the engine and it would therefore take a very long time until the vapor bubble in the pressure line is compressed, which would result in long startup times in order to start the engine, the published, non-examined German patent disclosure DE 195 39 885 A1 proposes that the first fuel pump delivers the fuel directly into the pressure line leading to the fuel valve, bypassing the second fuel pump. However, since the first fuel pump is designed for the normal operating state of the engine, a determination had to be made that the startup process proposed in DE 195 39 885 A1 does in fact lead to a considerable shortening of the startup time that is not, however, short enough under all circumstances that all conceivable desires are fulfilled as a result.